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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


URBANA,  JULY,    1902. 


BULLETIN  NO.  77. 


*BITTER  ROT  OF  APPLES. 


BY  THOMAS  J.  BURRILL,  CHIEF  IN   BOTANY,  AND  JOSEPH   C.   BLAIR,   CHIEF 

IN  HORTICULTURE. 

There  is  no  other  disease  which  is  so  enormously  destructive  to  the 
apple  fruit  as  is  the  one  commonly  called  "bitter  rot."  Its  ravages  at 
times  constitute  a  veritable  pestilence,  so  that  apparently  within  a  few 
days  the  richest  promise  of  the  finest  crop,  perhaps  almost  mature,  re- 
sults in  nothing  but  a  mass  of  corruption  and  calamitous  disappoint- 
ment. It  occurs  over  a  very  wide  area  of  the  American  continent 
from  Maine  to  Texas,  and  perhaps  everywhere  that  apples  are  grown  ; 
but  its  effects  seem  to  be  serious  only  in  southerly  regions.  In  Illinois, 
though  the  disease  has  been  found  much  further  north,  it  has  not  caused 
alarming  destruction  far  above  the  39th  parallel  of  north  latitude,  or 
much  north  of  Effingham  and  Jerseyville.  It  is  altogether  possible, 
however,  that  pestilential  outbreaks  of  the  disease  may  sometimes  oc- 
cur further  northward,  at  least  there  is  nothing  known  to  prevent  the 
spread  of  the  pest  throughout  the  state. 

The  disease  so  far  as  its  effects  are  concerned  has  been  long  known 
and  its  ravages  in  Illinois  a  quarter  of  a  century  ago  were,  in  proportion 

*On  July  I4th  Circular  No.  58  was  issued  from  this  Experiment  Station,  entitled 
"  Prevention  of  Bitter  Rot."  This  circular  gave  what  information  there  was  at 
hand  at  that  time,  and  the  fruit  growers  were  advised  to  search  for  and  remove  as 
speedily  as  possible  all  diseased  apples  and  cankered  limbs. 

351 


352  BULLETIN  NO.  JJ. 

to  the  area  of  orchards  existing,  as  great  and  as  direful  as  at  any  sub- 
sequent time.  The  worst  outbreak  in  quite  recent  years  occurred  in 
1900,  when  it  was  estimated  that  $1,500,000.00  worth  of  fruit  was  de- 
stroyed upon  the  trees  in  four  counties  of  our  state,  where  investiga- 
tions were  more  especially  made.  Presumably  the  losses  were  as  great 
in  other  apple  growing  regions  subject  to  the  disease. 

Infected  apples  have  already  been  found  this  year  (July  24,  1902) 
in  nine  counties,  all  except  Champaign  lying  south  of  the  line  men- 
tioned, but  extending  entirely  across  the  state.  Commonly  the  disease 
works  its  baneful  destruction  later  in  the  season,  during  August  and 
September,  though  it  may  be  inferred  that  its  earlier  appearance  has 
heretofore  escaped  observation.  Attention  has  been  especially  given 
to  it  this  year.  The  first  record  of  its  existence  on  young  apples  was 
made  June  28th,  but  the  specimens  showed  that  the  infection  must 
have  been  at  least  two  weeks  earlier,  and  it  has  been  otherwise  suffi- 
ciently proved  that  in  numerous  instances  the  attack  occurs  as  soon  as 
the  middle  of  June. 

The  rapidity  of  development  depends  upon  climatic  conditions.  It 
is  essentially  a  hot  weather  disease,  and  moisture  is  necessary  for  the 
distribution  and  germination  of  the  spores.  It  is  true  that  the  infec- 
tion of  the  fruit  sometimes  becomes  apparent  and  the  progress  of  the 
disease  is  abundantly  evident  when  the  atmosphere  is  very  dry;  but  this 
only  happens  after  the  fungus  has  gained  entrance  to  the  apples,  which 
must  have  occurred  during  a  previous  period  of  rainy  weather.  Rain 
and  high  temperature  are  necessary  to  start  an  epidemic.  These,  of 
course,  are  only  favorable  conditions  for  the  development  of  the  fungus 
which  is,  itself,  the  direct  agent  of  destruction.  Fortunately  the  latter 
is  not  very  resistant  to  unfavorable  conditions  and  may  die  out  entirely 
during  one  year  where  it  has  been  previously  abundant.  This,  with  its 
power  of  enormous  multiplication  under  circumstances  well  suited  to  its 
growth,  sufficiently  accounts  for  the  marked  irregularity  in  the  time 
and  virulence  of  its  attack. 

THE  DISEASE  UPON  THE  FRUIT. — Anyone  who  cares  to  do  so  may 
readily  identify  the  disease  as  it  occurs  on  growing  apples.  The  points 
of  infection  vary  from  one  to  a  countless  number,  commonly,  however, 
from  one  to  not  more  than  a  half  dozen.  At  first  these  are  minute, 
brown  specks  ;  later  they  enlarge  so  as  to  make  each  a  conspicuous, 
dark-colored,  circular  spot,  which,  while  preserving  its  circular  form  and 
maintaining  a  sharply  defined  border,  gradually  extends  to  become. per- 
haps an  inch  or  more  in  diameter.  The  affected  area  does  not  become 
soft,  but  is  soon  depressed  or  somewhat  sunken  while  the  skin  assumes 
a  leatherly  appearance.  The  outer  portion  of  the  spot  remains  smooth 
and  polished  while  the  central  area  looses  its  lustre  and  becomes 


I9°2.J  BITTER  ROT  OF  APPLES.  353 

roughened  by  the  formation  of  a  raultitade  of  minute  pustules  arranged 
in  irregular,  concentric  circles.  When  the  atmosphere  is  not  too  dry  each 
of  these  little  pustule  opens  and  there  exudes  in  microscopic  masses, 
or  columns,  a  waxy  substance,  which  is  at  first  pale  pink  in  color,  then 
pale  dull  red,  or  at  length  grayish  when  long-  exposed  to  the  sun.  The 
spot  ultimately  becomes  shriveled  in  appearance,  tough  in  texture,  and 
very  dark— approaching  black — in  color.  When  there  are  to  begin 
with  several  spots  they  run  together  but  commonly  preserve  some  indi- 
cation of  the  original  centers  of  each  in  the  general  area  of  infection. 
The  diseased  apple  finally  becomes  dark  brown  throughout,  and 
shriveled  into  a  dry,  hard,  and  much  wrinkled  mass  called  a  "mummy." 
This  may  remain  firmly  attached  to  its  twig  on  the  tree  for  a  year  or 
more,  but  commonly  falls  to  the  ground  before  the  drying  process  is 
entirely  completed. 

The  exuding  material  from  the  little  pustules  is  at  first  of  the  con- 
sistence of  thick  mucilage,  and  in  this  condition  that  from  neighbor- 
ing pustules  may  run  together  in  masses  of  still  small,  but  variable 
size.  In  dry  weather  the  substance  becomes  harder  and  forms  little 
waxy  crusts  adherent  to  the  surface  of  the  fruit.  At  no  time  does  this 
become  dusty  or  capable  of  being  carried  by  the  wind.  An  appeal  to 
the  microscope  shows  that  the  material  is  composed  of  myriads  of  ob- 
long, thin- walled  spores,  each  of  which  is  capable  of  starting  by  germ- 
ination and  penetration  of  the  skin  of  an  apple  an  infected  spot  like 
that  from  which  it  came.  The  substance  which  renders  them  adhesive 
and  keeps  the  mass  when  dry  together  is  very  soluble  in  water.  When 
placed  in  a  drop  of  this  liquid  the  spores  readily  separate  from  each  other 
and  are  then  easily  distributed  in  any  degree  of  dilution  with  the  fluid. 
This  characteristic  must  be  borne  in  mind  in  the  discussion  to  follow 
and  in  connection  with  the  methods  recommended  for  the  prevention 
of  the  disease.  It  is  worthy  of  note  that  while  the  spores  are  imbedded 
in  the  waxy  masses  and  kept  dry  they  retain  their  vitality  during  many 
weeks  and  even  months,  but  when  once  dissolved  in  water  subsequent 
drying  kills  them.  If  kept  moist  they  germinate  and  then  quickly  per- 
ish if  they  do  not  find  the  proper  nutriment.  It  is  impossible,  there- 
fore, that  these  spores  should  long  retain  their  vitality  when  exposed 
to  the  weather,  and  altogether  unlikely  that  they  ever  live  over  winter 
out  of  doors.  After  one  infected  apple  begins  to  produce  spores  the 
disease  may  be  spread  on  the  tree  by  the  splashing  of  rain  drops,  or  the 
adhesive  spores  may  be  readily  carried  by  insects.  It  is  now  well  un- 
derstood, however,  that  the  progress  of  infection  from  tree  to  tree  in 
an  orchard  is  usually  slow,  and  sbill  slower  from  orchard  to  orchard. 
Sporadic  cases  are  always  liable  to  occur,  of  which  the  origin  cannot  be 
traced;  but  the  idea  that  the  disease  starts  suddenly  throughout  a  large 


354  BULLETIN  NO.  ~J. 

area  where  it  had  no  existence  previously  is  not  tenable,  and  can  only 
have  been  held  by  anyone  through  faulty  observations. 

How  DOES  THE  FtiNGus  PASS  THE  WINTER  ? — Until  recently 
nothing  has  been  known  as  to  where  and  how  the  parasite  passes  the 
winter  and  how  the  first  infection  of  summer  occurs.  In  Bulletin 
69  of  the  Agricultural  Experiment  Station  of  the  University  of  Illinois, 
issued  in  February,  1902,  George  P.  Clinton,  Assistant  Botanist,  gave 
the  results  of  his  studies  during  July,  August,  and  September  of  the 
preceding  year.  He  showed  that  the  fungus  produced  a.  second  form 
of  fruit  or  spores  in  artificial  cultures  and  that  these  spores  developed, 
under  certain  conditions,  on  old  diseased  apples  (mummies).  From 
this  he  inferred,  without  chance  however  to  verify  the  supposition,  that 
the  fungus  lived  through  the  wintenon  such  mummified  apples  and  that 
the  newly  found  second  kind  of  spores  produced  the  primary  infection 
of  the  succeeding  year.  That  this  may  sometimes  be  true  is  quite  pos- 
sible; it  is  even  probable,  but  further  observations  have  not  so  far 
established  the  fact. 

During  the  autumn  of  1901  Mr.  H.  Hasselbring  of  the  Illinois 
Agricultural  Experiment  Station  took  up  the  work  as  it  was  left  by  Mr. 
Clinton.  Many  diseased,  shrivelled  apples  (mummies)  were  collected 
and  kept  under  different  conditions  for  studies  during  the  winter  and 
spring.  Hasselbring  never  found  the  second  spore-forms  described  by 
Clinton  on  such  apples  kept  out  of  doors,  but  he  has  found  that  the 
fungus  ordinarily  retains  its  vitality  in  a  dormant  state  in  the  winter 
and  in  May,  or  later,  under  proper  conditions  begins  to  produce  again 
the  same  kind  of  spores,  borne  on  fertile  threads  of  the  fungus,  in  the 
same  manner  as  it  did  the  praceding  summer.  Spores  so  secured  from 
old  mummies  were  inoculated  into  green  apples  on  June  8th  of  the 
present  year  and  produced  typical  bitter  rot  spots.  This  was  repeated 
with  spores  from  bitter  rot  mummies  collected  in  different  parts  of 
the  state  and  was  found  to  be  an  easy  procedure.  The  spring  infection 
may  therefore  start  from  these  old  apples,  and  recent  observations  in 
the  field  have  given  indisputable  evidence  that  it  does  sometimes  so 
occur. 

It  is  a  fact,  however,  that  the  bitter  rot  mummies  usually  fall  from 
the  tree,  and  the  question  has  been  a  puzzling  one  how  the  spores,  not 
capable  of  being  carried  by  the  wind,  can  rise  from  the  ground.  There 
is  indeed  no  proof  that  they  do  this.  The  supposition  that  they  are 
carried  by  insects  is  purely  speculative.  In  multitudes  of  cases  the 
disease  starts  where  no  mummy  remains  on  the  tree.  It  has  been  long 
observed,  however,  that  the  early  infection  on  a  tree  took  the  form  of 
a  triangle  or  cone  as  shown  by  the  spots  on  the  apples.  At  the  apex 
of  this  area  one  or  two  green  apples  commonly  show  rot  spots  larger 


IQ02.]  BITTER    ROT  OF  APPLES.  355 

and  older  than  those  below,  and  the  inference  was  a  most  natural  one 
that  these  fruits  gained  infection  from  spores  produced  on  old  mum- 
mies, and  that  other  apples  beneath  them  received  spores  carried  in  rain 
water  from  those  first  infected.  Still  the  explanation  was  wanting  as 
to  how  these  fruit  spores  were  carried  from  the  old  mummies  on  the 
ground  to  the  upper  parts  of  the  tree,  and  Hasselbring  found  this  year 
that  the  most  careful  collection  and  destruction  of  these  old  diseased 
fruits  failed  to  prevent  outbreaks  of  the  disease. 

All  this  was  held  in  rnind  when  the  undersigned  started  on  a  trip 
of  inspection  and  study  through  the  main  apple-producing  regions  of 
the  state.  Anything  whatever  touching  the  origin  and  development 
of  the  disease  was  considered  highly  important  and  received  the  ut- 
most attention.  On  July  llth  Captain  R.  A.  Simpsonf  of  Vincennes, 
Indiana,  expressed,  in  answer  to  a  question,  the  opinion  that  the  dis- 
ease on  the  earliest  affected  apples  upon  a  given  tree  was  traceable  in 
each  case  to  an  old  rough  wound  on  one  of  the  branches,  and  going 
with  us  to  trees  having  infected  fruit  he  pointed  out  in  several  cases 
that  just  above  the  area  of  infection  there  was  usually  to  be  found 
such  a  wound-spot  on  a  limb.  This  was  a  new  observation J  and 
Simpson's  discovery  was  quickly  taken  up  for  verification.  Further 
search  in  various  orchards  gave  continuously  increasing  support  to 
the  probable  correctness  of  this  supposition,  and  microscopic  exami- 
uations  made  July  12th  and  13th  in  the  Station's  laboratory  at  Salem, 
Illinois,  contributed  greatly  towards  a  confirmation  of  the  connection 
between  cankered  places  on  the  limbs  and  the  disease  upon  the  fruit  ; 
for  it  was  found  that  many  spores,  identical  with  those  from  the  mi- 
nute pustules  of  the  rot-spots  on  apples  were  exuding  in  the  familiar, 
pinkish,  waxy  masses  in  places  from  the  dead  bark.  Further  examina- 
tion showed  that  these  bark-borne  spores  originate  from  the  free  ends  of 
closely  clustered  threads  of  the  fungus,  just  as  those  from  the  mum- 
mied apples  are  produced.  This  is  clearly  shown  in  figures  9  and  10 
drawn  from  nature  by  Mr.  Hasselbring.  Inoculations  made  July  13th, 
in  green  apples  of  spores  taken  from  cankers  on  limbs  produced  in 
four  days  typical  bitter  rot. 


tMr.  Simpson  had  direct  supervision  of  spraying  experiments  for  bitter  rot 
last  year  at  Parkersburg  and  Odin  conducted  jointly  by  the  Illinois  Experiment 
Station  and  the  Division  of  Vegetable  Physiology  and  Pathology  of  the  United 
States  Department  of  Agriculture,  and  this  year  has  charge  of  similar  experi- 
ments at  the  former  place  for  the  above  named  Division  under  the  direction  of 
Dr.  Herman  Von  Schrenk. 

JOn  July  I4th  Mr.  W.  P.  Storment  of  Kell,  Illinois,  showed  one  of  us  a  can- 
kered limb  which  he  had  cut  from  a  tree  and  from  which  he  had  tried  the  previ- 
ous week  to  infect  apples  by  applying  to  their  surfaces  water  with  which  the  can- 
ker had  been  washed.  His  observations  had  led  him  to  suspect  that  the  early 
infection  of  the  fruit  came  from  the  limb  canker. 


356  BULLETIN  NO.  77.  [  July, 

It  therefore  became  evident  that  the  disease  on  apples  could  come 
from  these  spots  on  the  branches,  and  everything  now  goes  to  show 
that  except  in  the  few  cases  that  the  rot  mummies  hang  over  winter 
on  the  trees,  the  first  or  early  infection  conies  solely  from  these  limb- 
cankers.  This  is  of  the  greatest  importance  in  connection  with  the 
prevention  of  an  outbreak  of  the  disease.  The  identification  and  re- 
moval of  the  affected  branches  is  not  difficult  and  if  done  in  time 
must  be  effectual  in  preventing  the  disease  on  the  fruit. 

BITTER  ROT  CANKER. — The  term  canker  is  a  convenient  one  for 
the  rough  wounds  made  by  the  fungus  on  limbs,  but  several  other 
kinds  of  corroding  or  spreading,  diseased  spots  on  the  bark  of  trees  are 
loosely  designated  by  this  name,  making  it  necessary  to  speak  of  this 
as  the  bitter  rot  canker.  It  is  altogether  different  in  origin  and  ap- 
pearance from  the  lk  Illinois  apple  tree  canker  "  described  in  Bulletin 
70  of  this  Station,  which  for  the  most  part  attacks  the  trunk  and 
larger  branches.  The  bitter  rot  canker  is  found  more  often  than  else- 
where on  limbs  from  a  half-inch  to  one  inch  in  diameter,  though 
sometimes  on  mere  twigs  or  fruit  spurs,  and  sometimes  on  limbs  twice 
or  more  the  maximum  size  given.  It  starts,  at  least  in  many  cases, 
from  a  mechanical  bruise  or  other  injury  to  the  bark.  Sometimes  the 
canker  is  found  as  a  ragged  border  to  the  rough  wound  made  by  break- 
ing a  limb  half  off.  No  doubt  it  often  starts  in  bruises  made  by  the 
ladder  at  the  time  of  gathering  fruit,  and  it  appears  in  some  cases  to 
begin  in  a  very  small  twig  and  then  run  down  to  and  spread  in  the 
bark  of  a  larger  limb.  The  wood  is  not  destroyed,  though  it  dies  un- 
der the  affected  bark.  Growth  takes  place  around  the  diseased  area  as 
it  does  about  any  wound,  and  there  is  formed  in  an  irregular,  encircling 
rim  of  healing  tissue  about  a  dead  and  depressed,  or  sunken,  usually 
elongated,  black  patch,  covered  with  dead  bark.  On  very  small  twigs 
the  rim  of  growth  may  be  slight  or  none,  but  the  spore-producing 
places  are  always  dead  and  dry  except  as  wet  with  rain.  At  this  sea- 
son of  the  year  (July)  the  fungus  does  not  seem  to  exist  in  the  living 
bark.  It  is  never  found  on  or  in  the  leaves.  The  canker  in  the  limbs 
is  commonly  at  least  only  one  year  old  ;  the  fungus  does  not  persist 
perennially  in  the  bark.  The  appearance  of  the  canker  can  best  be 
learned  from  the  illustrations,  figures  4  to  8. 

Old  trees  long  infested  with  the  fungus  may  have  many  cankered 
spots  on  the  limbs,  and  certain  varieties — the  Huntsman  for  instance — 
are  liable  to  have  numerous  diseased  branches;  but  it  now  seems  to  be 
commonly  true  that  the  cankers  are  few  in  number,  at  least  upon 
the  kinds  of  trees  ordinarily  planted  in  Illinois  and  not  over  15  years 
of  age.  Only  a  tree  here  and  there  in  orchards  in  which  the  disease 
was  prevalent  one  and  two  years  ago  is  now  found  to  have  any  indi- 


IO02.]  BITTER  ROT  OF  APPLES.  357 

cations  whatever  of  the  malady.  The  spots  on  the  apples  can  now  be 
easily  seen  by  looking  closely  for  them,  but  the  cankers  are  not  easy  to 
discover  in  the  leafy  tree  without  some  guide  to  their  location.  As 
before  said  the  early  infected  apples  appear  beneath  the  cankered  spots 
on  the  limbs  and  spread  through  the  branches  in  a  cone-shoped  area; 
if,  therefore,  the  spotted  apples  can  be  seen,  the  canker  may  be  sought 
at  the  apex  of  the  cone,  and  experience  proves  that  it  can  in  most  cases 
be  easily  found  in  this  way.  Figure  1. 

PREVENTIVE  MEASURES. — From  the  results  so  far  obtained  by  this 
Station,  and  from  the  recent  experience  of  several  practical  orchardists 
the  following  preventive  measures  are  recommended: 

The  orchard  should  be  examined  systematically,  following  the 
rows  tree  by  tree  and  making  the  sharpest  possible  search  for  the  rot 
spots  on  the  apples.  It  is  best  that  the  examination  be  made  from  an 
elevated  position  so  as  to  look  down  upon  the  fruit  as  much  as  is  possi- 
ble, the  first  infection  taking  place  on  the  upper  surface  of  the  apple 
as  a  rule.  Drive  down  between  the  rows  with  a  spraying  outfit,  having 
two  men  stand  upon  the  operator's  platform,  a  man  looking  at  each 
side.  Drive  slowly,  and  if  an  apple  looks  suspicious,  drive  closer  so  that 
a  careful  examination  can  be  made  Figure  11  shows  three  men 
at  work  making  an  examination  in  the  Schwartz  Brothers1  orchard  at 
Salem.  Seventy  acres  of  orchard  were  critically  examined  in  this  way 
in  less  than  three  days.  After  the  infected  trees  have  been  located 
trace  all  of  the  Diseased  apples  until  the  cankered  limb,  which  is  the 
source  of  infection,  has  been  found.  These  infected  limbs  and  fruit 
should  be  removed  from  the  orchard  and  burned.  Figure  1  shows  a 
cankered  limb  at  X  just  below  the  knife,  which  is  sticking  in  the  limb. 
Looking  at  the  fruit  (in  the  angle  made  by  the  lines)  from  this  source 
of  infection  one  can  see  the  spotted  apples.  These  spots,  however, 
have  been  somewhat  darkened  in  the  photograph  so  as  to  bring  out 
more  clearly  their  condition.  The  work  of  removing  fruit  and  limbs 
should  be  done  cautiously,  so  as  not  to  spread  infection.  The  operator 
who  goes  into  the  tree  top  should  be  careful  not  in  any  way  to  cause 
the  rupture  of  the  bark. 

In  orchards  where  bitter  rot  has  not  yet  made  its  appearance,  but 
where  there  seems  to  be  some  likelihood  from  past  experience  of  its 
making  its  appearance,  it  would  be  well  to  be  on  the  safe  side  and  give 
a  thorough  application  of  Bordeaux  mixture. 

During  the  present  year  the  University  of  Illinois  has  been  carry- 
ing on  experiments  with  bitter  rot  in  orchards  at  Tonti,  Flora  and 
Tamaroa.  This  work,  together  with  results  obtained  from  the  experi- 
ments conducted  last  year,  and  reported  in  Circular  No.  43  of  the  Ex- 
periment Station,  prove  conclusively  that  spraying  with  Bordeaux  mix- 


358  BULLETIN  NO.  77.  [  July, 

ture  before  bitter  rot  makes  its  appearance  upon  the  fruit,  is  a  means  of 
holding  the  disease  almost  absolutely  in  check. 

Only  a  brief  statement  of  these  results  can  be  made  at  the  present 
time.  The  details  will  be  left  for  a  separate  publication  to  be  issued 
when  the  season's  work  is  completed. 

In  an  orchard  at  Tonti,  where  part  of  our  experiments  are  in  pro- 
gress, it  was  found,  on  July  8th,  that  bitter  rot  had  developed  on  un- 
sprayed  trees,  while  those  which  had  been  sprayed  every  ten  days  up  to 
June  17th  had  no  infected  fruit.  In  this  same  orchard  Ben  Davis 
trees  which  had  been  sprayed  showed  no  evidence  of  bitter  rot,  while 
an  occasional  infected  apple  could  be  found  on  those  trees  receiving  no 
spray.  From  two  unsprayed  Huntsman  trees  there  were  takeu  on  July 
9th,  647  infected  apples,  while  from  a  tree  which  had  received  Bor- 
deaux mixture  every  ten  days  there  were  but  6  infected  apples  ;  or  54 
rotten  apples  per  tree  where  there  was  no  spraying  as  against  one  where 
the  trees  were  treated.  On  July  12th  it  was  still  found  that  bitter  rot 
had  not  further  developed  on  the  sprayed  trees,  either  Ben  Davis  or 
Huntsman,  while  on  the  unsprayed  the  disease  was  spreading  rapidly. 
On  July  19th  but  three  infected  apples  were  taken  from  the  sprayed 
areas,  while  on  the  unsprayed  areas  the  disease  had  become  well  estab- 
lished on  a  greater  portion  of  the  fruit. 

The  exact  percentage  of  fruit  saved  by  spraying  will  be  clearly 
determined  when  the  records  are  compiled  at  the  end  of  the 
season's  work — records  which  will  have  been  secured  from  three  com- 
mercial orchards.  It  seems  certain,  however,  that  spraying  which  is 
started  now  in  orchards  reasonably  free  from  the  disease  will  do  much 
to  stop  the  progress  of  bitter  rot. 

A  limb  taken  from  an  infected  tree,  and  yet  which  was  well 
sprayed,  is  shown  in  figure  12.  It  will  be  noticed  that  this  fruit, 
which  is  well  covered  with  the  spraying  mixture,  is  entirely  free  from 
the  disease. 

The  fruit  grower  himself  must  be  the  judge  as  to  whether  or  not 
the  condition  existing  in  his  orchard  warrants  spraying  or  the  removal 
of  the  diseased  limbs  and  fruit.  In  most  orchards  it  is  quite  probable 
that  both  methods  should  be  employed. 

In  order  entirely  to  free  an  orchard  from  bitter  rot,  it  is  more  than 
likely  that  winter  pruning  and  spraying  will  be  the  proper  procedure. 
At  that  season  of  the  year  the  diseased  limbs  would  be  more  easily  de- 
tected, and  at  that  season,  also,  a  strong  solution  of  pure  copper  sul- 
phate can  be  applied  to  the  twigs  and  branches.  It  is  probable  that  in 
this  way  the  disease  can  be  stamped  out.  at  least  in  most  localities,  and 
at  comparatively  very  little  cost. 


IQ02.] 


BITTER  ROT  OF  APPLES. 


359 


FIGURE  i. 
TRIANGULAR  DISTRIBUTION  OF  ROT  IN  TREES,  AND  SOURCE  OF  INFECTION  ATX- 


FIGURE  2. 
THE  CANKERED  LIMB  SHOWN  IN  FIG.  i  AND  ALSO 

SOME  AFFECTED  APPLES   FROM  IT.      FKU1T 
PICKED  SEVERAL  FEET   BELOW  THK 
SOURCE  OF  INFECTION. 


FIGURE  3. 

DISEASED  APPLES  TAKEN 
FROM  INFECTED  AREA 

SHOWN  IN  FlG.   I. 


BULLETIN  NO,  JJ. 


\Jufy, 


FIGURE  4. 
A  CANKERED  LIMB  WITH  DISEASED  APPLES  BENEATH  IT. 


FIGURE  5. 
A  BITTER  ROT  CANKER. 


1 902.] 


BITTER  ROT  OF  APPLES. 


FIGURE  6. 
TYPES  OF  BITTER  ROT  CANKER- 


FIGURE  7. 
DISEASED  APPLES  AND  CANKERED  LIMBS. 


BULLETIN  NO.  77. 


July.. 


FIGURE  8.      BITTER  ROT  CANKER. 

'       ' 

. 


FIGURE  9.     PUSTULE  OF  BITTKR  ROT  FUNGUS  ON  MUMMIFIED  APPLE. 
SPORES  IN  OPENING  ABOVE.    ( HASSELBRING.) 


FIGURE  10. 
PART  OF  A  PUSTULE  FROM  BITTER  ROT  CANKER  ON  LIMB.    (HASSELBRIXG.) 


BITTER  ROT  OF  APPLES. 


363 


FIGURE  11. 
LOCATING  TREES  INFECTED  WITH  BITTER  ROT. 


FIGURE  12. 
SPRAYED  APPLES  FREE  FROM  BITTER  ROT. 


364 


BULLETIN  NO.  JJ. 


{July, 


•  mm  mgum  *  . 


JJlFFERhNT  STAGES  OF  BlTTER  ROT.      (CLINTON.) 


IQ02.]  BITTER  ROT  OF  APPLES.  365 

SUMMARY. 

LOSSES  CAUSED  BY  BITTER  ROT. 

Bitter  rot  is  a  disastrously  destructive  disease  upon  the  apple  fruit. 
It  has  prevailed  at  times  over  very  large  areas  of  the  territory  of  the 
United  States,  but  is  especially  liable  to  occur  south  of  the  39th  paral- 
lel of  north  latitude.  In  Illinois  in  1900  the  loss  in  four  counties  was 
estimated  to  be  $1,500,000.00  and  as  great  proportionally  to  the  acres  in 
orchards  elsewhere. 

APPEARANCE  OF  DISEASED  APPLES. 

The  disease  on  the  fruit  can  be  easily  identified.  Plate  C,  page  364. 
It  begins  in  one  to  many  brown  specks  anv  where  upon  the  unbroken 
skin  of  the  apple  and  each  point  of  infection  enlarges  so  as  to  become  a 
very  distinct,  dark-colored,  circular  and  somewhat  sunken  spot,  be- 
neath which  the  tissues  are  dry  (never  soft  and  watery)  and  tough. 
Great  numbers  of  pustules  so  small  as  to  be  scarcely  visible  to  the  un- 
aided eye,  arranged  in  close  concentric  circles  cover  all  but  the  outer 
border  of  the  discolored  spot  and  give  to  the  surface  a  roughened  ap- 
pearance. In  very  dry  weather  these  pustules  are  merely  minute, 
raised,  dark-colored  points,  but  when  the  air  is  sufficiently  moist  each 
conically  shaped  point  opens  by  breaking  through  the  skin  of  the  fruit 
and  discharges  a  little  pinkish  mass  of  a  mucilaginous  or  waxy  sub- 
stance well  seen  under  a  lens.  This  material  may  at  length  form  a 
reddish,  minutely  roughened  crust.  Each  spot  may  remain  distinct 
or  several  on  one  apple  may  run  together  so  as  to  form  an  irregularly 
shaped,  depressed  patch.  The  whole  fruit  at  length  becomes  shriveled 
into  an  angular,  hard  body  called  a  'k  mummy."  It  does  not  further 
decay. 

THE  DISSEMINATION  OF  THE  DISEASE. 

The  pinkish  or  reddish  material  from  the  spots  in  the  fruit  is  com- 
posed of  myriads  of  spores.  These  cannot  be  distributed  by  the  wind 
because  they  are  held  together  and  to  the  fruit  by  an  adhesive  sub- 
stance, which,  however,  is  very  soluble  in  water.  The  spores  are  car- 
ried in  splashes  of  rain  water  or  may  be  distributed  by  insects.  The 
fungus  lives  over  winter  in  the  old,  dried  fruits  (mummies)  and  in 
wound-like  infected  spots,  called  bitter  rot  cankers,  on  the  limbs  of  the 
tree.  During  the  month  of  May  or  later  a  fresh  crop  of  spores  may  be 
produced  from  the  mummies  and  from  the  limb  cankers.  The  former 
more  often  fall  from  the  tree.  The  first  infection  of  the  season  appa- 
rently comes  from  the  cankers  and  can  be  traced  on  the  young  apples 


366  BULLETIN   NO.   JJ.  [Jufy> 

spreading  below  these  in  cone-shaped  figures  in  the  trees,  where  the 
spores  have  been  carried  by  rain. 

The  disease  goes  slowly  from  tree  to  tree  in  an  orchard,  probably 
through  the  agency  of  insects. 

PREVENTION  OF  THE  DISEASE. 

At  this  season  of  the  year  (July)  and  later  where  the  disease  has 
not  become  widely  spread,  search  should  be  eystem  atically  made  in  the 
orchard  for  infected  trees  as  determined  by  the  spots  on  the  apples. 
This  can  best  be  done  from  an  elevated  position  like  the  platform  of 
a  spraying  outfit.  If  diseased  apples  are  found  the  infecting  canker 
(or  mummy)  should  be  looked  for  just  above  the  uppermost  of  the 
spotted  fruit.  The  canker  and  infected  fruit  should  be  removed,  tak- 
ing care  not  to  distribute  the  infection  in  the  process.  This  is  of  the 
utmost  importance  if  the  contagion  is  to  be  stopped. 

In  the  winter  time  the  mummies  and  cankers  can  be  removed  or 
the  fungus  probably  destroyed  by  spraying  the  trees  with  copper  sul- 
phate. 

The  disease  can  be  kept  in  check  during  tne  summer  by  repeated 
applications  of  Bordeaux  mixture. 


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